1. Field of the Invention
This invention relates to an agricultural tractor having high vertical clearance.
2. Description of the Prior Art
Agriculture has a tremendous need for tractors having various characteristics. This need has been met primarily by building a wide variety of tractors, including wheeled and tracked, of various heights and configurations. For example, wheel tractors are typically cheaper to run and faster, but cause increased soil compaction. Tracked tractors have better traction and soil compactiion characteristics, but the width of the tractor base cannot be modified.
Tractors typically need to run through fields discing, harrowing, spraying, weeding, cultivating and maintaining the contours of the rows and furrows. To allow field access many crops are planted in rows between furrows. The wheels or tracks pass down the furrows. The passage down the furrow causes compaction of the soil which interferes with irrigation and root propagation. The height of the plants and vertical clearance of the tractor determines the point at which the tractor can no longer enter the field until harvest. Frequently, furrow spacing becomes a function of the tractors rather than what is best for crop yield.
Tractor weight and distribution has an effect on soil compaction and an effect on what equipment and tools a particular tractor can carry or pull through a field. Weight is both a blessing and a curse. Weight improves traction which is of added importance in dealing with a wet or soggy field by providing earlier access. On the other hand, weight increases soil compaction. Distribution of weight is important to avoid lifting the front of a tractor off the ground and avoiding unnecessary compaction. This especially is a problem with wheel tractors where if the front wheels leave the ground, the tractor cannot be steered.
Distribution of weight will also change during a day's spraying as a spray tank empties. Efforts to deal with weight distribution such as placing spray reservoirs forward of the back wheels is a trade off. Such placement reduces visibility and can also interfere with repair and maintenance of the engine. Use of additional wheels known as duals to reduce compaction and increase traction is also a trade off, as maintenance is made more difficult and an uneven field can lead to broken axles.
Visibility is important. If a tractor veers from a furrow damage to the crop occurs. Similarly, the better a driver may observe a field as he moves through, the more likely problems can be detected early and better handled.
The wheel base of wheel tractors can usually be varied to some degree, but to make the change is cumbersome and time consuming. Many wheel tractors have an axle extending outward from the body of the tractor along which the wheel may be attached at various points. A drawback is that the vertical clearance is limited to 1/2 the size of the wheel minus 1/2 the diameter of the axle because the axle passes through the center of the wheel. Larger wheels increase clearance but in turn are heavier, more cumbersome and expensive.
Not all fields are level and the center of gravity and weight distribution of a tractor can limit the direction a tractor moves safely.